Method for synthetically making diamond



Aug. 8, 1967 Filed June 28, 1963 HIROSHI ISHIZUKA 3,334,968

METHOD FOR SYNTHETICALLY MAKING DIAMOND 3 Sheets-Sheet 1 5/PAV/V .F/ZE (Mas/0 l NVENTOR BY g M ATTORNEY Aug. 8, 1967 HIROSHI ISHIZUKA METHOD FOR SYNTHETICALLY MAKING DIAMOND 5 Sheets-Sheet Filed June 28, 1963 0 w 0 w 0 w w W 6 5 RQ QMQQ WPQ INVENTOR HIRDSHI \SH)ZUKA BY .M\5W

ATTORNEY Aug. 8, 1967 HIROSHI ISHIZUKA 3,334,963

I METHOD FOR SYNTHETICALLY MAKING DIAMOND Filed June 28, 1963 I 3 Sheets-Sheet 5 INVENTOR Hmosm \smzu A BY 2 M s m ATTORNEY United States Patent 01 METHOD FOR SYNTHETICALLY MAKING DIAMOND Hiroshi Ishizuka, 106 S-chome, Hiratsuka, Shinagawa-ku, Tokyo, Japan Filed June 28, 1963, Ser. No. 291,464

Claims priority, application Japan, June 30, 1962,

37/ 27,423 8 Claims. (Cl. 23209.1)

The present invention relates to improvements in or relating to a method for synthetically making diamond.

It is known to synthetically make diamond by combining graphite with a metal catalyst selected from the class consisting of iron, cobalt, nickel, rhodium, ruthenium, palladium, osmium, iridium, chromium, tantalum and manganese, subjecting the aforesaid graphite and metal 3,334,968 Patented Aug. 8, 1967 ice . required for the synthesis of the diamond in case the fine catalyst to a pressure of at least about 75,000 atmospheres and at a temperature of from about 1,200" to about 2,000 C., and isolating the formed diamond.

In the synthesis of diamond from graphite, it is desirable to provide methods which can utilize pressures less than 75,000 atmospheres so as to reduce the wear on the apparatus employed in the synthesis.

It is also known that the above result has been achieved by combining graphite with a preformed alloy catalyst of a metal selected from the class consisting of iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, chromium, tantalum and manganese, subjecting the aforesaid graphite and catalyst to a pressure of at least about 50,000 atmospheres and a temperature of at least about 1,200 C., and isolating the formed diamond.

It is an object of the present invention to provide a method whereby graphite may be converted to diamond at a pressure of less than about 75,000 atmospheres without the use of the preformed alloy cata'lyst.

I have now found that when graphite is converted into diamond by subjectnig graphite and iron, nickel or cobalt to an elevated temperature and pressure, the smaller the contact surface of graphite with iron, nickel or cobalt, the lower the temperature and pressure required for the synthesis of the diamond, and that on the basis of the above discovery, when the conversion of graphite into diamond is effected by employing iron, nickel or cobalt in the form of particles and by inhibiting the contact of the graphite with the iron, nickel or cobalt particles by mixture with fine powders of titanium, vanadium, molybdenum, tantalum, tungsten, chromium or manganese carbides, the diamond yie'ld can be obtained at a lower temperature and a lower pressure.

According to the present invention, therefore, I provide a method for synthetically making diamond wherein a mixture of particles of graphite and particles of a metal selected from the group consisting of iron, nickel and cobalt together with fine powders of the carbide of a metal selected from the group consisting of titanium, vanadium, molybdenum, tantalum, niobium, tungsten, chromium and manganese is subjected to a pressure of from about 75,500 to about 75,000 atmospheres at a temperature of from about 1,200 to about 1,600 C., the contact of the graphite with the metal particles being inhibited by the presence of the fine powders of the metal carbide.

The invention may be understood by reference to the following description taken in connection with the accompanying drawing in which:

FIG. 1 is a graph showing the relation between the grain size of nickel particles and the pressure required for synthesis of the diamond and also the relation between the grain size of the nickel particles and the pressure powders of carbide are used;

FIG. 2 is a graph showing the relation between the temperatures and the pressures which are used in the practice of the method of present invention;

FIG. 3 is an enlarged, sectional view of the reaction chamber in apparatus which may be used in the practice of the method of present invention.

In FIG. 1 of the drawing, the line A shows the relation between the grain size of nickel particles and the pressure required for the synthesis of the diamond, and the line B shows the relation when fine powdered chromium carbide is added. As shown in FIG. 1, the pressure required for the synthesis of diamond becomes low as the grain size of the nickel particles becomes large, and the pressure required is lower when the fine powder of chromium carbide is added.

This fact is also true in the case of iron and cobalt particles.

In FIG. 2 of drawing, the line AB is the thermodynamic pressure-temperature equilibrium line between diamond and graphite, the region between the line AB and the line CD is the diamond and graphite coexisting region and the region in the triangle LMN shows the pressure and temperature ranges which can be used in the practice of the method of present invention. It may be observed in FIG. 2 that the diamond can be synthesized under a pressure of less than 75,000 atmosphere in the method of present invention.

In FIG. 3 of drawing, 1 and 2 are pistons made of tungsten carbide-cobalt alloy containing 5% Co each of which is tapered at an angle of 27 from the vertical and has a face diameter of 15 mm. 3 is a ring made of tungsten carbide-cobalt alloy containing 6% Co which is applied with pressure and which has an inner diameter of 22 mm. 4 is a cylinder which is made of well baked magnesia which has a porosity of about 10% and an inner diameter of 15 mm. 5 and 6 are upper and lower rings made of annealed carbon steel. 7 and 8 are insulating plates made of pyrophyllite. 9 and 10 are conductors made of iron or nickel. 11 is a reaction mixture to be treated. 12 is an insulating cylinder made of pyrophyllite. 13 and 14 are graphite plates each of which covers one end of the insulating cylinder 12. 15 and 16 are insulating gaskets. Pressure is applied to the reaction mixture 11 by the pistons 1 and 2. Heating is effected by passing an electric current through 1, 5, 9, 13, 11, 14, 10, 6 and 2 in the order given.

The grain size of the iron, nickel and cobalt particles which may be used in the method of present invention is preferably larger than at least mesh, normally larger than 50 mesh, specially about 20 mesh, but it is suitable to use metal particles having a grain size larger than the above mesh when the size of the reaction chamber becomes large.

The grain size of the powders of titanium, vanadium, molybdenum, tantalum, niobium, tungsten, chromium and manganese carbides which may be used in the method of present invention is preferably smaller than at least mesh, normally smaller than 200 mesh, specially about 325 mesh.

The particle size of the graphite which is used in the method of present invention is preferably in the range of from the size of the metal particles to that of the carbide powders and is normally from about 40 to about 100 mesh.

In order to inhibit contact between the metal particles and graphites, said metal particles may be first mixed with the fine carbide powders and then mixed with the graphite particles. Alternatively the fine carbide powders and graphite particles may be mixed together first. By such mixing, the contact between the metal particles and the graphite particles can be inhibited, because the fine carbide powders cover both the surfaces of the metal particles and graphite particles.

In the method of present invention, the pressure may be maintained at a pressure of from about 57,500 to about 75,000 atmospheres and temperature may be maintained at a temperature of from about 1,200 to about 1,600 C. The theoretical reason for which the conversion into diamond of graphite can be practically effected under the above pressure at the above temperature is unclear, but in fact the diamond can be obtained as shown in the examples hereinafter given.

In the method of present invention, the reasons for which the special metal carbide powders are used is that the absorption of carbon by the metal particles may be limited and the synthesis of the diamond may be accelerated by the presence of the carbide powders. The carbide powders are not decomposed during the formation of the diamond.

The value of pressure which is applied in the method of present invention is measured by conventional indirect means in which the fact that certain metals undergo distinct changes in electrical resistance at particular pressures is utilized, as described in US. Patent No. 2,947,610.

In the method of present invention, the rate of conversion of graphite into diamond is fastest when iron particles are used, is medium in the case of nickle particles and is slowest for cobalt particles. When nickel or cobalt particles are used the crystals of diamond obtained are not so good and they are densely coloured. This type of diamond can be suit-ably employed for resin-bonding. On the other hand, when iron particles are used, the crystals of diamond obtained are good and are slightly coloured. This type of diamond can be suitably employed for metalbonding.

In the method of present invention, instead of particles of iron, nickel or cobalt, particles of iron, nickel or cobalt alloyed with non-metals, for example carbon, silicon or phosphorus may be used.

In the method of present invention, moreover, when the conversion of graphite into diamond is effected by maintaining the temperature in the central portion of reaction mixture at a temperature which is nearest to the temperature at which the conversion can'be effected and maintaining the operating pressure at a pressure which corresponds to the former temperature in the ranges of temperature and pressure which are used in the present invention, and then by gradually increasing the temperature in the central portion of reaction mixture in the temperature range of from about 300 to 500 C., the conversion is firstly effected in the central portion of reaction mixture to obtain diamonds and is progressively effected towards the outer portions of the reaction mixture to progressively obtain diamond formation without the occurrence of the reverse-conversion of diamond into graphite. Therefore the diamond can be synthesized in. high yield with the employment of lower pressure.

It is considered that this fact is due to the presence of diamond-graphite co-existing region in the outside of the diamond stable region which is surrounded by lines AB and CD as shown in FIG. 2 of the drawing, and that the conversion of graphite into diamond and also the reverse conversion into graphite may be not effected in the diamond-graphite co-existing region. The above technique may be also applied for other diamond synthesis methods.

The present invention is illustrated by the following examples with reference to the drawing.

Example I 500 mg. of nickel particles of 20-30 mesh, 100 mg. of chromium carbide powders of smaller than 325 mesh and 300 mg. of graphite of 100 mesh were mixed. The mixture was charged into the cylinder 12 and the cylinder 12 was sealed with graphite plates 13 and 14. This cylinder was placed as shown in FIG. 3. When the mixture was heated at the following temperatures under the following pressures, the yields of diamonds were as follows:

Pressure Temperature Yield (atrn.) 0-) t-L) In this example, when the pressure was maintained at the pressure of 70,000 atmospheres and the reaction temperature was successively increased from 1,400 to 1,700 C. for 20 minutes, the diamond was obtained in the yield of 25 0 mg.

In this example, when chromium carbide powder was not used, the diamond was not formed.

Example 2 The procedure of Example 1 was repeated with the exception that 500 mg. of iron particles of 20-30 mesh, mg. of manganese carbide powders of smaller than 325 mesh and 300 mg. of graphite of 100 mesh were used. The results obtained were as follows:

Pressure Temperature Yield (atm.) 0.) (mg.)

Example 3 The procedure of Example 1 was repeated with the exception that 500 mg. of cobalt particles of 20-30 mesh, 55 mg. of tungsten carbide powders of smaller than 325 mesh and 300 mg. of graphite of 40-50 mesh were used. The results obtained were as follows:

Pressure Temperature Yield (atm.) 0.)

In this example, when tungsten carbide powder was not used, the diamond was not formed.

Example 4 The procedure of Example 1 was repeated with the exception that 540 mg. of nickel particles of 2030 mesh, 60 mg. of vanadium carbide powders of smaller than 325 mesh and 300 mg. of graphite of 40-50 mesh were used. The results obtained were as follows:

Pressure Temperature Yield (atm.) 0.) (mg) Example 5 The procedure of Example 1 was repeated with the exception that 540 mg. of nickel particles of 20-30 mesh, 60 mg. of titanium carbide powders of smaller than 325 mesh and 300 mg. of graphite of 40-50 mesh were used. The results obtained were as follows:

Pressure Temperature Yield (atm.) 0.) a)

Example 6 Pressure Temperature Yield (ntm.) 0.) (mg) In this example, when tantalum carbide powder was used, the similar results were obtained.

Example 7 The procedure of Example 1 was repeated with the exception that 540 mg. of nickel particles of 20-30 mesh, 60 mg. of molybdenum carbide powders of smaller than 325 mesh 300 mg. of graphite of 40-50 mesh were used. The results obtained were as follows:

Pressure Temperature Yield (913111.) 0.) a)

Example 8 Pressure Temperature Yield (atm.) 0.) e)

Comparative Example 1 The procedure of Example 1 was repeated with the exception that 100 mg. of nickel particles of 20-30 mesh, 100 mg. of chromium carbide particles of 20-30 mesh and 300 mg. of graphite of 100 mesh were used. The results obtained were as follows:

Pressure Temperature Yield (atm.) C (mg) 75, 000 1, 550 Not formed. 72, 500 1, 500 Do.

Comparative Example 2 The procedure of Example 1 was repeated with the exception that 500 mg. of nickel powders of 325 mesh, 100 mg. of chromium carbide particles of 20-30 mesh and 300 mg. of graphite of 100 mesh were used. The result obtained was as follows:

Comparative Example 3 The procedure of Example 1 was repeated with the exception that 500 mg. of nickel powders of 200 mesh, 100 mg. of chromium carbide powders of smaller than 325 mesh and 300 mg. of graphite of 100 mesh were used. The result obtained was as follows:

Pressure Temperature Yield (atm.) 0.) e) 75, 000 1, 500 Not formed.

What I claim is:

1. The method of forming a synthetic diamond which comprises the steps of a forming a mixture consisting essentially of particles of graphite, particles of a metal selected .from the group consisting of iron, nickel and cobalt and the carbide in powder form of a metal selected from the group consisting of titanium, vanadium, molybdenum, tantalum, niobium, tungsten, chromium and manganese, the quantity of said powder being sufficient to inhibit contact between said particles of graphite and particles of metal; subjecting said mixture to a pressure in the range from about 57,500 to about 75,000 atmospheres; and heating said mixture to a temperature in the range from about 1,200 to about 1,600 C. while maintaining said mixture subjected to said pressure.

2. The method according to claim 1, wherein said step of forming said mixture is performed by first mixing said particles of metal and said powder and thereafter adding said particles of graphite.

3. The method according to claim 1, wherein the size of said particles of metal is in the range from about to 20 mesh.

4. The method according to claim 1, wherein the size of the particles of said powder is in the range from about mesh to about 325 mesh.

5. The method according to claim 1, wherein the size of said particles of graphite is in the range from the size of said particles of metal to the size of the particles of said powder.

6. The method according to claim 1, wherein the size of said particles of graphite is in the range from about 40 to about 100 mesh.

7 .The method according to claim 1, wherein said group consisting of iron, nickel and cobalt is alloyed with at least one member of the group consisting of carbon, silicon and phosphorous.

8. The method of forming a synthetic diamond which comprises the steps of: forming a mixture consisting essentially of particles of graphite having a size in the range from about 40 to about 100 mesh, particles of a metal selected from the group consisting of iron, nickel and cobalt, said particles of metal having a size in the range from about 20 mesh to about 80 mesh, and at least one carbide of a metal selected from the group consisting of titanium, vanadium, molybdenum, tantalum, niobium, tungsten, chromium and manganese, said carbide being in the form of a powder having a particle size in the range from about 7 8 100 mesh to about 325 mesh, said powder being first References Cited mixed separately with one of said types of particles before UNITED STATES PATENTS the other type is introduced into mlxture for inhibiting contact between the particles of the two types; subject- 2,947,609 8/1960 Strong ing said mixture to a pressure in the range from about 5 2,992,900 7/1961 Bovenkerk 23 209-1 57,500 to about 75,000 atmospheres; and heating said mix- 3,148,161 9/1964 Wentorf et a] 252 502 ture to a temperature in the range from about 1,200 to I about 1,600 C. while maintaining said mixture subjected OSCAR VERTIZ Prlmary to said pressure. E. I. MEROS, Assistant Examiner. 

1. THE METHOD OF FORMING A SYNTHETIC DIAMOND WHICH COMPRISES THE STEPS OF; FORMING A MIXTURE CONSISTING ESSENTIALLY OF PARTICLES OF GRAPHITE, PARTICLES OF A METAL SELECTED FROM THE GROUP CONSISTING OF IRON, NICKEL AND COBALT AND THE CARBIDE IN POWDER FROM OF A METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM, VANADIUM, MOLYBDENUM, TANTALUM, NIOBIUM, TUNGSTEN, CHROMIUM AND MANGANESE, THE QUANTITY OF SAID POWDER BEING SUFFICIENT TO INHIBIT CONTACT BETWEEN SAID PARTICLES OF GRAPHITE AND PARTICLES OF METAL; SUBJECTING SAID MIXTURE TO A PRESSURE IN THE RANGE FROM ABOUT 57,000 TO ABOUT 75,000 ATMOSPHERES; AND HEATING SAID MIXTURE TO A TEMPERATURE IN THE RANGE FROM ABOUT 1,200* TO ABOUT 1,600*C. WHILE MAINTAINING SAID MIXTURE SUBJECT TO SAID PRESSURE. 